The calculator
Crop factor equivalents for your lens
Change any input and the results update instantly. Select your sensor format to see the crop factor applied.
Lens & aperture
In millimeters — the number printed on your lens (e.g. 50, 85, 24).
The f-stop marked on your lens — e.g. 1.8, 2.8, 5.6, 11.
Sensor format
Each format has a fixed crop factor — see the reference table below.
Equivalent: at
How it works — the formulas in full
Two formulas. Both multiply by the crop factor. The distinction between them is important: one describes field of view, the other describes depth of field — and neither changes your exposure settings.
Variable definitions
What each symbol means
FL — focal length in millimeters, as printed on the lens.
N — the f-number (aperture). A dimensionless ratio: focal length divided by entrance-pupil diameter.
CF — crop factor. A dimensionless multiplier expressing how much smaller the sensor is compared to a 35 mm full-frame sensor. Full frame = 1.0; APS-C 1.5× = 1.5; Canon APS-C 1.6× = 1.6; Micro Four Thirds = 2.0; 1-inch = 2.7.
EFL — equivalent focal length. The focal length a full-frame lens would need to produce the same field of view.
EAP — equivalent aperture. The f-number a full-frame lens would need to produce the same depth of field and gather the same total light across the sensor area. This is a comparison value — it is not the f-number you dial in for exposure.
Equations
CROP_FULL_FRAME = 1.0 // 35 mm full frame — the reference
CROP_APS_C_1_5 = 1.5 // Nikon, Sony, Fuji APS-C
CROP_CANON_APS_C = 1.6 // Canon APS-C (slightly smaller sensor)
CROP_MICRO_4_3 = 2.0 // Micro Four Thirds (Olympus, Panasonic)
CROP_ONE_INCH = 2.7 // 1-inch sensor (Sony RX100, Nikon CX, etc.)
EFL = FL × CF
Multiply your lens focal length by the crop factor. A 50 mm lens on APS-C 1.5× gives EFL = 50 × 1.5 = 75 mm. This describes field of view — how zoomed-in the image looks compared to a full-frame shot. The lens focal length does not physically change.
EAP = N × CF
Multiply your f-number by the crop factor. A 50 mm f/1.8 lens on APS-C 1.5× gives EAP = 1.8 × 1.5 = f/2.7. This tells you: to match the depth of field you get from this APS-C setup on a full-frame camera, you would need a 75 mm f/2.7 lens.
Critical: your f/1.8 lens still exposes exactly as f/1.8 on the APS-C body. Do not apply the equivalent aperture to your metering, shutter speed, or ISO. Crop factor does not change the amount of light reaching each pixel — it changes how much of the image circle the sensor captures.
Crop factor constants — the full reference
These are the fixed constants this calculator uses. The crop factor for each format is derived from the ratio of the 35 mm full-frame diagonal (43.3 mm) to the sensor's diagonal. The active row is highlighted when you select a format above.
| Sensor format | Crop factor | Sensor diagonal (approx.) | 50 mm becomes | f/1.8 DoF equiv. |
|---|---|---|---|---|
| Full frame (35 mm) | 1.0× | 43.3 mm | 50 mm | f/1.8 |
| APS-C 1.5× (Nikon, Sony, Fuji) | 1.5× | 28.4 mm | 75 mm | f/2.7 |
| Canon APS-C 1.6× | 1.6× | 26.7 mm | 80 mm | f/2.9 |
| Micro Four Thirds 2× | 2.0× | 21.6 mm | 100 mm | f/3.6 |
| 1-inch sensor 2.7× | 2.7× | 15.9 mm | 135 mm | f/4.9 |
The "f/1.8 DoF equiv." column shows the equivalent aperture for a physical f/1.8 lens on each format — this is for depth-of-field comparison only. Your exposure remains f/1.8 regardless of sensor format. Sensor diagonals are approximate; crop factors are conventional rounded values used across the industry.
Worked example — step by step
A 50 mm lens at f/1.8 on an APS-C 1.5× camera. These match the calculator's default inputs — every figure below can be verified by hand in seconds.
Inputs
50 mm · f/1.8 · APS-C 1.5×
FL = 50 mm | N = 1.8 | CF = 1.5 (APS-C 1.5×)
Step 1 — Identify the crop factor
The sensor is APS-C 1.5× (Nikon, Sony, or Fuji body). From the constants table:
CF = 1.5 — this sensor is 1.5× smaller than full frame in linear dimension.
Step 2 — Equivalent focal length
EFL = FL × CF
EFL = 50 × 1.5
EFL = 75 mm
A 50 mm lens on this APS-C body frames a scene identically to a 75 mm lens on full frame.
The lens has not changed; the sensor is cropping the image circle.
Step 3 — Equivalent aperture (depth of field comparison only)
EAP = N × CF
EAP = 1.8 × 1.5
EAP = f/2.7
To produce the same depth of field as this APS-C f/1.8 setup on a full-frame camera,
you would need a 75 mm lens set to f/2.7. The APS-C sensor's smaller size means it
has inherently more depth of field for the same field of view.
Step 4 — Confirm your actual exposure is unchanged
The f/1.8 lens is still f/1.8 for metering purposes. Your camera meters at f/1.8, your shutter speed and ISO reflect f/1.8 — nothing about the exposure calculation changes. The equivalent aperture f/2.7 is a system-comparison number used when evaluating how this APS-C kit compares to a full-frame kit for background blur or low-light depth-of-field control. It is not a value you enter into your camera.
Step 5 — Interpret the results
A 50 mm f/1.8 on APS-C 1.5× is equivalent in framing to a 75 mm f/2.7 on full frame. That means: you get the field of view of a short telephoto but with more depth of field than a full-frame shooter using the same framing. Background blur will be less pronounced than a true 75 mm f/1.8 full-frame setup — a common source of confusion for photographers moving between systems.
Common mistakes with crop factor
Crop factor is a simple multiplication, but the surrounding concepts trip up even experienced photographers. These are the errors that show up most often.
Thinking the lens physically changes or "zooms in"
The lens does not change when mounted on a smaller sensor. Its focal length, aperture, and optical characteristics are fixed. What changes is the field of view recorded by the sensor — a smaller sensor captures a smaller area from the center of the image circle, which looks like a crop of the full-frame image. The phrase "acts like a 75 mm lens" is shorthand for field of view only; the glass behaves exactly as a 50 mm lens at all times.
Applying the equivalent aperture to exposure settings
The equivalent aperture (f-number × crop factor) is a depth-of-field comparison value. It is not a correction to make to your camera. If you shoot f/1.8 and then set your camera to f/2.7 because of the "equivalent aperture," you will underexpose by over a full stop. Your metering, shutter speed, and ISO should always reflect the actual f-number on your lens, which in this case is f/1.8.
Forgetting that the sensor crops, not magnifies
A common mental model is that a crop sensor "magnifies" the image — this is not quite right. The lens projects the same image circle it always projects. The crop sensor simply records a smaller portion of it. The effect on field of view is the same as cropping in post-processing and enlarging — you see less of the scene, but the physics of the lens have not changed. Understanding this distinction helps when thinking about resolution: a crop sensor captures fewer pixels from the lens's full image circle.
Using the wrong crop factor for Canon vs. other APS-C bodies
Not all APS-C sensors are identical. Most manufacturers (Nikon, Sony, Fuji) use a 1.5× crop factor, but Canon APS-C sensors are slightly smaller and use 1.6×. The practical difference is small — a 50 mm lens becomes 75 mm on a Nikon APS-C body and 80 mm on a Canon APS-C body — but when shooting at the edge of a focal length for a specific purpose (shooting sports at a 400 mm threshold, for example), the 6% gap matters. Always check which body you are working with.
Expecting the same background blur as a full-frame equivalent focal length
A 50 mm f/1.8 on APS-C gives the field of view of 75 mm but not the background blur of 75 mm f/1.8 on full frame. The depth of field is equivalent to a 75 mm f/2.7 full-frame setup — noticeably more depth of field, noticeably less background separation. Photographers who switch from full frame to a crop system expecting the same subject isolation are often disappointed. Use the equivalent aperture value to set realistic expectations before choosing a system or a lens.